The present invention relates to a process for making a continuous structure of a composite material.
It is known that the spreading of composite materials is becoming increasingly more extended in several different technical fields due to the good features of same in terms of mechanical strength, stiffness, capability of reaching a good heat sound and electric insulation, good resilience, and others. In more detail, panels made of composite materials which are increasingly more required on the market find application either as covering elements for furniture or indoor fittings, or as structural parts such as ribs or frames for shell constructions, or as parts of means of transport, and so on.
Under this situation, different types of structures in the form of panels made of a composite material capable of meeting the most various requirements have been developed. These structures are differentiated from each other both for the different material types employed and the different arrangement of the reinforcing fibers within the resin matrix.
In the present treatment reference will be particularly made to panels of a composite material comprising a resin matrix within which a three-dimensional reinforcing structure is incorporated which is made of textile fibers comprising two external layers interconnected by intermediate connecting threads.
These types of panels are presently manufactured starting from a semifinished textile product, made of fiberglass for example, which substantially has the same sizes as the intended panels.
The semifinished product is then impregnated with resin and inserted between two mold halves of a press after interposing a pair of plates, each of which faces one of the external layers of the semifinished product.
Subsequently, after fixing the plates to the respective mold halves, said halves are partly closed in order to promote a homogeneous distribution of the resin. Afterwards, a partial polymerization is carried out for fixing said plates to the external layers of the impregnated semifinished textile product. At this point, the mold halves, together with said plates, are moved apart from each other by a predetermined distance so that the connecting threads of the two layers in the semifinished textile product move from a first condition in which they are substantially reclined and arranged parallel to the external layers, to a second condition in which they are disposed substantially perpendicular to the external layers themselves.
Finally a complete polymerization of the resin is carried out followed by drawing of the composite structure out of the mold.
While the above described process enables the achievement of panels of a composite material having good mechanical features and a good degree of surface finish, it also has many drawbacks.
First of all it is to note that since the process is carried out by molding, due to its own nature only single-size panels can be made. Therefore, it is necessary to have as many molds as there are panels to produce or, alternatively, to arrange sufficiently extended molds for producing panels of relatively large sizes which are then conveniently cut. However, in the last mentioned case many important problems arise both as regards construction and economy, since molds of great sizes are to be made and consequently presses capable of operating said molds are needed.
It should be also recognized that the above described molding process is very slow and therefore enables very low production rates to be achieved, which results in higher costs of the final product, also taking into account the fact that, when the polymerization step is completed, a further step of drawing the panels out of the mold halves is always necessary.